1. Field of Invention
The present invention relates generally to the field of oilfield exploration, production, and testing, and more specifically to protection of pump components used in such ventures.
2, Related Art
Electrical submersible pumps (ESPs) are used for artificial lifting of fluid from a well or reservoir. An ESP typically comprises an electrical submersible motor, a seal section (sometimes referred to in the art as a protector) which functions to equalize the pressure between the inside of the system and the outside of the system and also acts as a reservoir for compensating the internal oil expansion from the motor; and a pump having one or more pump stages inside a housing. The protector may be formed of metal, as in a bellows device, or an elastomer, in which case the protector is sometimes referred to as a protector bag.
A variety of production fluids are pumped from subterranean environments. Different types of submersible pumping systems may be disposed in production fluid deposits at subterranean locations to pump the desired fluids to the surface of the earth. For example, in producing petroleum and other useful fluids from production wells, it is generally known to provide a submersible pumping system for raising the fluids collected in a well. Production fluids (e.g., petroleum) enter a wellbore drilled adjacent a production formation. Fluids contained in the formation collect in the wellbore and are raised by the submersible pumping system to a collection point at or above the surface of the earth.
In addition to motors, pump sections, and seals, a typical submersible pumping system may further comprise a variety of additional components, such as a connector used to connect the submersible pumping system to a deployment system. Conventional deployment systems include production tubing, cable and coiled tubing. Additionally, power is supplied to the submersible electric motor via a power cable that runs through or along the deployment system.
Often, the subterranean environment (specifically the well fluid) and fluids that are injected from the surface into the wellbore (such as acid treatments) contain corrosive compounds that may include carbon dioxide, hydrogen sulfide, and brine water. These corrosive agents can be detrimental to components of the submersible pumping system, particularly to internal electric motor components, such as copper windings and bronze bearings. Moreover, irrespective of whether or not the fluid is corrosive, if the fluid enters the motor and mixes with the motor oil, the fluid can degrade the dielectric properties of the motor oil and the insulating materials of the motor components. Accordingly, it is highly desirable to keep these external fluids out of the internal motor fluid and components of the motor.
Submersible electric motors are difficult to protect from corrosive agents and external fluids because of their design requirements that allow use in the subterranean environment. A typical submersible motor is internally filled with a fluid, such as a dielectric oil, that facilitates cooling and lubrication of the motor during operation. As the motor operates, however, heat is generated, which, in turn, heats the internal motor fluid causing expansion of the oil. Conversely, the motor cools and the motor fluid contracts when the submersible pumping system is not being used.
In many applications, submersible electric motors are subject to considerable temperature variations due to the subterranean environment, injected fluids, and other internal and external factors. These temperature variations may cause undesirable fluid expansion and contraction and damage to the motor components. For example, the high temperatures common to subterranean environments may cause the motor fluid to expand excessively and cause leakage and other mechanical damage to the motor components. These high temperatures also may destroy or weaken the seals, insulating materials, and other components of the submersible pumping system. Similarly, undesirable fluid expansion and motor damage can also result from the injection of high-temperature fluids, such as steam, into the submersible pumping system.
Accordingly, this type of submersible motor benefits from a motor fluid expansion system able to accommodate the expanding and contracting motor fluid. The internal pressure of the motor must be allowed to equalize or at least substantially equalize with the surrounding pressure found within the wellbore. As a result, it becomes difficult to prevent the ingress of external fluids into the motor fluid and internal motor components.
Numerous types of motor protectors have been designed and used in isolating submersible motors while permitting expansion and contraction of the internal motor fluid. A variety of elastomeric bladders alone or in combination with labyrinth sections have been used as a barrier between the well fluid and the motor fluid. For example, expandable elastomeric bags or bladders have been used in series to prevent mixing of wellbore fluid with motor fluid while permitting expansion and contraction of the motor fluid. Another type of protector employs a bellows, such as a one-piece annular bellows.
As may thus be seen, there remains a need in the natural resources exploration and production field for improving reliability and life of motor protectors. The present invention is directed at providing such protectors.